I am trying to model a controls mixing unit on an aircraft and I need a special function to do this and I can't think of one for the life of me! I have a ruddervator, which serves as a rudder and elevator. Basically I need the following: - For a pure rudder input, I get a linear change in rudder +/- 20 deg. - For a pure elevator input, I get a linear range in elevator for +/- 20 deg. - For any combination of elevator and rudder, the two need to be mixed (by what amount depends on the function you give me). Ideally, they are weighted equally for equal amounts of inputs. BUT, you cannot exceed 20 degrees deflection of the surfaces, that is their physical limits! So your function has an upper and lower bound. The last one is easy, its having the simultaneous requirement of the first two points which makes life difficult! If you cant satisfy all three as linear, just give me whatever you got anyways - it might stimulate some ideas in that space between my ears.